With only three days until Christmas in 2003, Frédéric Mazzella was under pressure to get to his family home in Fontenay-le-Comte, 300 miles outside Paris – but all the trains were full.

After eventually getting a lift from his sister, he noticed most of the cars on the road were empty but for the driver. This was a vast inefficiency in his eyes – but one that got him thinking.

"The idea was to organise all the available seats in cars just like we organise all the available seats in planes and trains, with a real search engine, and this did not exist. There was only demand and no offer and organised in a very weird way in that you would have neighbours who would share a ride but you did not know where they were going and when," he says.

Mazzella's observation that day was the seed for the car-sharing company BlaBlaCar, and it has grown to the point at which the president of SNCF, the French national railway, identified it as a competitor last year.

The Paris-based company has six million members in a dozen countries, linking drivers with passengers who can buy seats. According to the company, a million people use its website every month, keying in details of where they want to go and when, and getting a list of drivers heading to the same destination, with their journey history and a price – which can be a fraction of a ticket on public transport.

Mazzella says the early years were marked by frustration as BlaBlaCar struggled to reach a critical mass of drivers and passengers who could meet each others' demands.

"You would have people offering a ride from Paris to Lyon on a Thursday at 6pm and people looking for a ride from Montpellier to Bordeaux on a Monday at 2pm," he says.

The turning point came in 2007 when a series of strikes crippled the French transport system. A well-timed press release to say BlaBlaCar was still open for business attracted huge media attention.

Nicolas Brusson, one of the three co-founders with Mazzella and Francis Nappez, says the influx of users meant that "suddenly the service worked". For the first time, people were saying things about the service such as "useful, interesting, low-cost, efficient".

After that leap forward, the business continued to grow, opening an office in 2009 and hiring its first employee. Then when the Icelandic volcano Eyjafjallajökull erupted in April 2010, throwing gigantic quantities of ash into the air and causing massive disruption to air travel, prices on BlaBlaCar skyrocketed. With a trip from Madrid to Paris costing €850 (£706), the founders decided to cap prices in an attempt to retain the spirit of the "sharing economy".

That decision also means drivers do not pay tax on the income as the price cap ensures they do not make a profit. In a similar vein, their insurance is not affected as it is not deemed a commercial venture.

These days when drivers offer a ride, an online calculator suggests the price with an upper limit – it costs around £35 to go from London to Edinburgh, for instance. Drivers can ask for more but the maximum is £46.

Profiles of members show how much experience they have of the service, meaning those with more – known as "ambassadors" – attract more ride shares and, importantly, each user's profile includes a "BlaBla" measurement, which indicates how much they are willing to chat during a trip.

In France, the company charges a commission of 11% of the journey price – something that will begin in the UK this year, where at the moment there are no charges. Recent expansion to Russia and Ukraine brings to 12 the number of countries where BlaBlaCar operates, the others being the UK, Spain, Portugal, France, Italy, Belgium, Luxembourg, Holland, Poland and Germany.

In January 2012, $10m (£6m) was raised in a venture round led by Accel Partners.

"We are learning to use our resources in a smarter way. Driving alone in your car for 300 miles has always been a nonsense, it is an economical and an ecological nonsense and it is boring," says Mazzella.

"It was just a business model from the automobile industry: they had one product – the Ford T [the first affordable car] was released with four seats – and it has always been the same product. They sold it to families at the beginning, then to the dad, the mum, the son. When [children] are 18, they will get one.

"It was always a social way of transport [but] then it became individual cars. Now cars when they are finished have one seat which is used and three [that] are not – it is a nonsense."

He says that car advertisements typically have one driver. "The message that is sent is that you can have one for your weekends, one for your weekdays – the entire auto industry is getting us to buy cars all the time.

"Half the TV ads are for the new car industry and it is 10% of the French domestic product. Cars spend 95% of their time not moving and the 5% of their time when they are moving, there is one person in it."

Students, artists, civil servants and teachers in their late 20s were the typical users at the outset but this has broadened as BlaBlaCar has grown, according to Mazzella.

The company may expand into Asia, the US and Latin America and the founders cite trains and buses as the competition, not similar services. BlaBlaCar is often compared to Airbnb, the six-year-old accommodation site that was recently reported to be in talks to raise capital in a deal valuing it at $10bn.

Brusson predicts that Europe is coming to the end of an era. "Every state except Germany is broke, so it is not like we are going to build new roads and rail networks. We need to be smarter about the way we consume and leverage the assets that we have already and make better use [of them]," he says. "I think we are entering an era of more efficiency. I think we are going to consume in a new way. The reality is now you can leverage your apartment and your car."

Sidebar – Is it safe?

BlaBlaCar carries out checks on the mobile phone numbers, emails and bank accounts of its users and encourages members of the community to rate each other, in turn building trust for frequent members.

"If you wanted to go and steal a car and do something weird, why would you bother to go on a site where you have to check your bank account and check your mobile number?" asked Brusson.

A feature called "Ladies Only" was introduced to allow for cars where both the drivers and passengers are female.